UD78 User Guide
Issue code: 78nu2
A-6
Example
To set parameter
1.25
at +76.4 for a Drive that is unit 6 of group 2, send:
Control Address Control Parameter Data Control BCC
EOT 2 2 6 6 STX 0 1 2 5 + 0 7 6 . 4 ETX %
A.5 Re-writing a parameter value
Once a write message which includes the address field has been sent to a
Drive and accepted with either a <
ACK
> or <
NAK
> response, subsequent
write messages to that particular Drive can use a re-write message structure
in which the address does not need to be re-transmitted. The re-write
structure is as follows:
STX M1 M2 P1 P2 D1 ... Dn ETX BCC
When a different Drive is addressed, or an invalid character is received, the
re-write facility no longer functions. The first Drive can be addressed again
only by using the full write message with the address.
A.6 Calculating the block checksum
(
BCC
)
The block checksum is calculated by applying an exclusive
OR
function to all
of the characters of a message after the
STX
control character.
XOR truth table
A
B
Out
0
0
0
0
1
1
1
0
1
1
1
0
Example
To set parameter
1.25
at –34.5
The first character of the
BCC
calculation is
0
(00110000 in binary), the value
of which is taken as a starting or result value. The next character is
1
(00110001 in binary), which now has the exclusive
OR
(
XOR
) operator act
upon it. With the previous result value, a new result occurs of 00000001 in
binary.
